<!DOCTYPE html>

<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>伪类选择器</title>
        <style type="text/css">
            .wrapper { width: 500px ; height: 100px ; border: 1px solid blue ; margin: 30px auto ; }
            .wrapper:hover { background-color: red ;  }
        </style>
    </head>
    <body>

        <div class="wrapper"></div>

        <div class="wrapper second"></div>

    </body>
</html>